Method of making soap



United States Patent METHOD OF MAKING SOAP Baruch Winer, Brooklyn, N. Y.

No Drawing. Application March 10, 1953, Serial No. 341,613

Claims. (Cl. 260-413) This invention relates to the manufacture of soap and more particularly to an improved method of making a soap of relatively low moisture content. It is generally recognized that low moisture content soaps are those soaps having a water content of less than about 15% by weight and the phrase low moisture content soap is used in the present specification and claims to describe and characterize such soaps. The present application is a continuation-in-part of my prior applications Serial No. 127,518, filed November 15, 1949, and Serial No. 282,271, filed April 14, 1952, now abandoned.

The classical method of soap making, which is still used extensively, involves heating fatty acid glycerides or free fatty acids or mixtures of fatty glycerides and fatty acids to form alkali metal salts of the fatty acids. In cases where the raw material contains glycerides, byproduct glycerine is produced which is commonly extracted with brine. In either event, the soap produced by such processes contains of the order of by weight moisture.

While soaps containing such a high moisture content can be used for some purposes, there are other applications for which such a high moisture content cannot be tolerated. Thus, for example, where the soap is to be ground to a powder or Where a flaked soap is to be produced a satisfactory product can be achieved only by using a low moisture content soap as defined above.

The problem of producing a low moisture content soap from a 30% moisture soap as prepared by the classical method referred to above is a diflicult one. Removal of water from the bulk soap by evaporation is not practical because of foaming problems and also because of the fact that the soap has a very low thermal conductivity and hence if it is heated in bulk form there is a tendency for the portions of the soap adjacent to the heating surfaces to decompose before any considerable amount of water has been removed from the mass by evaporation. Hence drying can be effected only by comminuting the soap to increase the surface area through which heat can be introduced. This may be done, for example, by spraying the soap into a stream of hot air or by other known methods. However, all such methods require specialized equipment and increase substantially the cost of producing the soap.

It is evident that an alternative approach to the problem of producing a low moisture content soap is possible, namely, carrying out the saponification reaction under such conditions that only a limited amount of water is added to the reaction mass so that a low moisture content soap is directly produced and no drying step is required. Various proposals along this line have previously been made but so far as I am aware none has been commercially satisfactory. Thus it has been proposed that the saponification of fatty acids be carried out with relatively concentrated aqueous caustic alkali containing say 25%5'0% by Weight of alkali metal hydroxide. But when the saponification is carried out in this manner "ice the reaction is so rapid that lumps are formed which entrap substantial amounts of the strong alkali and the lumpiness of the reaction mass prevents adequate contact between the fatty material and alkali.

If, on the other hand, weaker alkalis such as dry sodium carbonate are used a substantial excess of the alkali must be added to achieve or approach complete saponification of the fatty acids. Moreover, sodium carbonate is incapable of saponifying the glycerides and hence cannot be used with raw materials containing substantial proportions of glycerides. While there are certain situations in which such a high alkali content can be tolerated, there are many other cases in which the soap product must not only have a low moisture content but must also be substantially neutral and substantially completely saponified.

It is accordingly an object of the present invention to provide an improved method of saponifying a fatty material to produce a low moisture content soap. It is another object of the invention to provide a method of making a low moisture content soap that is substantially neutral and substantially completely saponified; that is, a soap product that contains no more than a fraction of a per cent of free alkali and unsaponified saponifiable matter. It is still another object of the invention to provide a method of this character that can be carried out in a continuous manner in relatively inexpensive equipment. It is a still further object of the invention to provide a method of making a low moisture content soap of high quality from undistilled fatty acids as a raw material. Other objects of the invention will be in part obvious and in part pointed out hereafter.

in one of its broader aspects, the present invention comprises a method of producing a low moisture content soap wherein the saponification is carried out in two stages. In the first stage a fatty acid mixture, or mixture of fatty acids and glycerides is reacted with a quantity of dry alkali metal carbonate that is sufficient to saponify a substantial proportion of the free fatty acids present in the raw material but insuificient to saponify all of the fatty materials present. Thereafter, in a second stage, saponification of the fatty material is completed with a concentrated aqueous caustic alkali.

I have found that by carrying out the saponification reaction under the controlled conditions described below and in two stages using dry alkali metal carbonate in the first stage and a caustic alkali in the second stage, the difliculties of the prior art processes as previously described can be avoided. Since the quantity of carbonate used is appreciably less than that required to saponify completely the fatty materials present the initial saponification step can be readily and quickly carried to completeness. Moreover, the physical condition of the reaction mass is such that the carbon dioxide produced in the saponification reaction can be substantially completely eliminated. I have found that the soap formed in the first stage of the reaction is completely compatible with the unreacted fatty acids and glycerides and mixes therewith to form a homogeneous mass. When this mass is subsequently treated with strong aqueous caustic alkali the relatively large proportion of soap therein inhibits the saponification reaction to such an extent that the reaction proceeds smoothly without lump formation to saponify the unreacted fatty acids as well as the glycerides. Moreover, since no water at all is added in the first stage of the saponification and since only a limited amount of Water is added in the second stage, a soap product is obtained having a moisture content sufficiently low so that no subsequent drying step is required to produce a low moisture content soap.

In a somewhat narrower aspect, the present invention comprises a method of making a low moisture content soap which includes the steps of reacting a fatty material composed predominantly of free fatty acids with an an hydrous alkali metal carbonate, preferably sodium carbonate, in an amount sufficient to saponify 30%80% by weight of the free fatty acid content of the fatty material and then completing saponification of the fatty material with an aqueous alkali metal hydroxide solution, preferably a sodium hydroxide solution, containing at least by weight of the hydroxide. I have found that my process is operative when the quantity of carbonate used is sufficient to saponify only about 30% of the free fatty acid in the raw material used. However, in most cases it is desirable to use a quantity of carbonate sutficient to saponify at least half, and preferably about 60% of the free fatty acids present.

The upper limit on the quantity of carbonate to be used is largely determined by the requirements of the product to be produced. Thus if the nature of the use to which the soap product is to be put is such that unreacted sodium carbonate can be tolerated therein, a quantity of carbonate can be used in the first stage of the saponification that is sufficient to saponify 80% of the free fatty acids or even somewhat more than 80%. On the other hand, if the specifications for the product require that the free alkali be no more than a fraction of a per cent, it is desirable to use a quantity of carbonate that saponifies somewhat less than 80% of the free fatty acids present in the raw material.

In carrying out the saponification reaction, it is desirable that the mass be heated to a temperature within the range of say 80 C. to 175 C. The preferred heating schedule in most cases is as follows: During the first stage of the saponification, the reaction mass is maintained at a temperature sulficient to keep the mass in liquid condition, so that the carbon dioxide formed as an incident of the reaction can escape more readily from the reaction mass. The precise temperature required to maintain the reaction mass liquid varies as a function of the nature of the fatty material used as a raw material and also as a function of the amount of carbonate added. As the proportion of carbonate is increased the viscosity of the mass at the end of the first stage of saponification also increases, and hence when a relatively large quantity of carbonate is used a higher temperature is required to maintain the reaction mass fluid, and vice versa. It may be noted that When the heating of the fatty material for the reaction is carried out in the absence of air, temperatures higher than 175 C. can be satisfactorily used. Also in particular cases temperatures as low as 60 C. have been found operative.

At the end of the first stage of saponification the mass is preferably cooled to a viscous dough-like consistency before the aqueous caustic alkali is added. I have found that when the second stage of the saponification is carried out at such a temperature that the reaction mass is quite viscous a relatively high concentration of caustic, say to 50% by weight, can be used without encountering difficulties because of lump formation. On the other hand if the second stage saponification is carried out at a temperature such that the reaction mass is liquid a more dilute caustic alkali solution must be used to prevent lump formation. Hence the cooling step between the first and second stage saponification is useful since it reduces the quantity of water added to the reaction mass and yields a product having a lower moisture content.

While the foregoing heating schedule is preferred in most cases, there are other situations where modification is desirable. For example, in the making of toilet soaps it is a common practice to add a perfume to the soap. When a perfume is to be added it is usually desirable to carry out the saponification reaction at a relatively low temperature to avoid vaporization of this additive.

It may be noted that the use of high temperatures is generally advantageous since they increase the heat content of the reaction mass and hence the heat available for evaporation of water from the mass. To the extent that such evaporation occurs, the moisture content of the final product is, of course, reduced.

in some cases it is desirable to preheat the reactants in order to increase the heat content of the reaction mass and thereby increase evaporation of Water therefrom. It may be further noted that where glycerides as well as fatty acids are present in the raw material and where the saponification is to be carried out on a continuous basis it is desirable to use a temperature of 140 C. or higher in the second stage to ensure a sufiiciently high saponification rate. The nature of the fatty material used as a raw material in the present process may vary widely, and in general any of the common soap-forming fatty materials can be used. Thus the raw material may be distilled fatty acids, or undistilled fatty acids or, in fact, any soap-forming mixture of glycerides and fatty acids, provided that the mixture contains a major fraction of free fatty acids. One widely used material, which is obtained by a conventional fat splitting process, comprises a mixture of glycerides and fatty acids containing about 10% to 15% by weight glycerides and 90% to by weight free fatty acids, and this material is well suited for use in my process. The preferred saponifying agents used in the two stages respectively are anhydrous sodium carbonate and aqueous sodium hydroxide but other alkali metal carbonates and hydroxides can be used if desired.

In many cases it is desirable that the product of the second stage saponification be recovered in pellet form, both because pellets provide a large surface area for evaporation of moisture and because the pellets can be readily ground to a powder. Pel-letizing of the reaction product can be effected by increasing the amount of alkali used in the second stage of the saponification, that is, using an amount appreciably in excess of that required to complete the saponification reaction. This increase in alkali can be achieved either by increasing the amount of caustic alkali used or by adding a variety of other alkalies such as, for example, sodium silicates, carbonates or phosphates.

In order to point out more fully the nature of the present invention, the following specific examples are given of illustrative methods of carrying out the invention:

Example 1.S0ap pellets 250 pounds of crude fatty acids containing about 10% by weight glycerides are heated to about 123 C. and then mixed in a strong crutcher or tilting dough mixer with about 37 pounds of soda ash. A vigorous reaction starts immediately and the carbon dioxide evolved raises the mass appreciably, but after a few minutes the mass settles back to the lower part of the mixer. The walls of the mixer should be scraped free of the incompletely saponified mass. The quantity of soda ash used is such as to provide about 60% saponification of the fatty acids present in the raw material. The reaction is completed in about 57 minutes and at the end of this time the reaction mass had a highly viscous dough-like consistency.

The mass is then treated with 50 pounds of 50% caustic soda solution which is preheated to a temperature of about C. and then divided into two portions. The first portion, comprising 45 pounds of the solution, is added at the beginning of the second stage saponification and the second portion, comprising 5 pounds, is added near the end of the reaction when the mass becomes very thick. The mixing is continued until the mass breaks up into pellets. The entire operation including filling and emptying of the mixer takes only 15 to 20 minutes.

The soap product resulting from the foregoing operation comprises 88% anhydrous soap, between 0.5 and 1% glycerine and the rest alkalies and moisture. It may be noted that the alkali used in the second stage of the saponification is considerably in excess of that required for saponification. This excess of alkali facilitates evaporation of water from the reaction mass and also increases the friability of the soap and thereby assists in the formation of pellets. The pelletized soap after cooling is in a convenient form and condition for grinding to form a soap powder.

Example 2.-Sap flakes Garbage grease having an acid number of 60 and a saponification number of 195 is used as a raw material. 100 pounds of the grease is heated to 175 C. and reacted with 6 pounds of dry sodium carbonate. Within 3-5 minutes the reaction of the carbonate and grease is complete and all of the carbon dioxide has been eliminated.

Thereafter, 20 pounds of a 50% caustic soda solution preheated to 150 C. is added. After 57 minutes a strong boiling action starts and a large amount of vapor comes out of the mixer which is externally heated by gas flames. After 2-3 minutes a plastic mass settles in the lower part of the mixer. The contents of the mixer is emptied over a three-roll mill of which the first roller is heated and the last two are water-cooled and the soap product is scraped from the roll surfaces in flake form. The moisture content of the recovered flakes is about 6%.

Example 3.T0ilet soap 100 pounds of distilled fatty acids comprising a mixture of 80% tallo-w acids and 20% cocoanut oil fatty acids is heated to 145 C. with stirring in a mixer and reacted with 10 pounds of dry soda ash, which is a quantity of soda ash sufficient to saponify about 50% of the fatty acids. The sap-onification reaction is completed and the carbon dioxide eliminated in the reaction mass in a few minutes. The soap fatty acid mixture is a dark colored solution.

Upon completion of the first stage saponification, a mixture of 13 pounds of 50% caustic soda, 8 pounds of water and 4 pounds of sodium silicate solution of 40 Baum, which solution has been preheated to 100 C., is added to the partially saponified fatty material and mixed therewith for about 2 minutes. Boiling of the reaction mass occurs and a large amount of steam is evolved. After one minute the soap mass settles to a homogeneous plastic mass. Perfuming and coloring materials can be added and mixed in at this stage, if desired.

The resulting soap product has a moisure content of about 15%, about 0.1% free alkali and no measurable unsaponified saponifiable matter.

Example 4-S0ap flakes A light-weight gas-heated mixer is charged with 100 pounds of undistilled fatty acids having an acid number of 190 and a saponification number of 204. The fatty acids are preheated to about 175 C. and then mixed with 15 pounds of dry soda ash, which is a quantity of soda ash suflicient to saponify about 75% of the free fatty acids of the raw material. Within ten minutes the first stage saponification is complete and all carbon dioxide has been eliminated.

The resulting liquid mixture of soap, fat and fatty acid is poured into an unheated dough mixer and permitted to cool with mixing for a period of about one minute. At the end of this period the liquid mixture has become congealed to a viscous dough-like mass. To this mixture 12 pounds of caustic soda solution is added. After about 3 minutes the reaction mass in the mixer starts to boil and a quantity of steam is evolved. At the end of an additional 2 minutes the reaction is complete and the reaction mass is in a homogeneous plastic condition.

The resulting product is converted into flake form as in Example 2 and has a moisture content of 8%, about 0.1% free alkali, and about 0.25% unsaponified saponifiable matter.

Example 5Soap powder pounds of undistilled fatty acids of yellow grease with an acid number of 190 and a saponificati'on number of 200 is preheated to 80 C. and charged into a heated mixer wherein the fatty acid mass is reacted with 15 pounds of dry soda ash. The reaction goes substantially to completeness in ten minutes with the major part of the carbon dioxide being evolved and eliminated. At the end of this period the reaction mass was a viscous mixture of soap, fat and fatty acid.

To this mixture 20 pounds of 50% caustic soda is added. After ten minutes of mixing the mass in the mixer starts to break into small pieces. The mixing is continued until all the soap is broken down to small pellets. During the period in which the mass disintegrates into pellet form a very large amount of water vapor continues to be evolved.

The resulting soap .pellets have a moisture content of about 8% and after cooling are ground in the usual manner to form a soap powder.

The foregoing examples illustrate the manner in which the different operating conditions can be varied within the scope of the invention to produce a number of different products. Thus in the case of the toilet soap of Example 3, it is important that the product be substantially neutral, whereas the requirement with respect to moisture content is less severe than in the case of soap powders. Also it is desirable that the temperature be kept relatively low to prevent vaporization of perfumes and to minimize odors due to thermal decomposition. In order to make sure that the react-ion mass remains liquid during the first stage sa-ponification and that the reaction proceeds to substantial completeness a relatively small amount of soda ash must be used.

Example 4, on the other hand, is concerned with the production of soap having a moisture content of only 8%. Hence a relatively larger amount of soda ash is used to increase the proportion of the saponification that is carried out with this anhydrous alkali. In order to ensure complete reaction and CO2 elimination with this larger amount of alkali a higher temperature is used. This relatively high temperature also increases the heat content of the reaction mass, and therefore the heat available for evaporation of moisture.

Example 1 illustrates the production of a product wherein excess alkali can be tolerated. The two stages of the saponification are carried out at approximately the same temperature and the quantity of soda ash used is suflicient to cause the reaction mass to become quite viscous at the end of the first stage. Thus a strong caustic alkali solution can be used without danger of lump formation during the second stage and suflicient excess alkali is used to pelletize the mass.

In Example 2 the fatty material contains a relatively large proportion of glycerides and hence a relatively small amount of carbonate is used. Under these conditions a temperature of about C. is suflicient to maintain the reaction mass liquid, but the higher temperature is used to store heat in the reaction mass that can be used in the second stage for evaporation of water from the mass. Example 2 further illustrates the use of a small amount of soda ash in the first stage in conjunction with the use of a relatively strong concentration of caustic in the second stage. This combination of conditions is possible because of the presence of a relatively large amount of glyceride that reduces the saponification rate in the second stage. If the procedure of Example 2 is used to produce a product that is to be ground into a powder, a caustic alkali concentration as high as 80% can be satisfactorily used.

From the foregoing description it should be apparent that the present invention provides an effective method of achieving the several objects set forth at the beginning of the specification. The two-stage saponification described herein provides a rapid and economical method 7 of producing a substantially neutral, low moisture content soap. While the foregoing examples illustrate batch "operations, it is apparent that the method is readily adapted to continuous operation as well.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment disclosed herein, it is to be understood that the foregoing description is to be interpreted as i1- lustrative only and not in a limiting sense.

I claim:

1. The method of making a soap containiu" not more than about 15% by weight moisture which comprises reacting a fatty material composed of free fatty acids and a maximum of about 15% glycerides with a dry alkali metal carbonate in an amount sufficient to saponify 30%80% by weight of the fatty acid content of said material at a temperature between about 60 and about 175 C., and then completing saponification of said material with an aqueous alkali metal hydroxide solution containing from 10% to about 50% by weight of said hydroxide.

2. The method of making a soap containing not more than about 15% by weight moisture which comprises reacting a fatty material composed of free fatty acids and a maximum of about 15% glyccrides with dry sodium carbonate in an amount sufficient to saponify 30%80% by weight of the fatty acid content of said material at a temperature between about 60 and about 175 C., and then completing saponification of said material with an aqueous sodium hydroxide solution containing from 10% to about 50% by weight of said hydroxide.

3. The method of making a soap containing not more than about 15% by weight moisture which comprises reacting with a fatty material essentially composed of fatty acids and a maximum of about 15% glycerides a quantity of dry alkali metal carbonate sufficient to saponify 30%80% by weight of the fatty acid content of said material at a temperature between about 60 and about 175 C., said quantity being insufficient to cause the viscosity of the reaction product to reach such a high value as to entrap a substantial amount of the carbon dioxide produced as a product of the reaction, and thereafter completing saponification of said material with aqueous caustic alkali having a concentration of 10% to about 50% by weight.

4. A method according to claim 3 and wherein the reactants are preheated to increase the amount of water evaporated from the reaction mass during the saponification.

5. The method of making a soap containing not more than about 15% by weight moisture which comprises mixing a fatty material composed of free fatty acids and a maximum of about 15% glycerides with a quantity of dry alkali metal carbonate sufficient to saponify 30%80% by weight of the fatty acid content of said material, heating the mixture of fatty acid and carbonate to maintain it in liquid condition at a temperature between about 60 and about 175 C. until the carbonate saponitication of the fatty acid is complete, and treating the resulting mixture with aqueous caustic alkali having a concentration of 10% to about 50% by weight to complete saponir'ication of said material.

6. A method according to claim 5 and wherein a mixture of fatty acid and carbonate is heated to a temperature between 80 C. and 175 C.

7. The method of making a soap containing not more than about 15% by weight moisture which comprises reacting a fatty material essentially composed of free fatty acids and a maximum of about 15% glycerides with a dry alkali metal carbonate in an amount sufhcient to saponify 30%80% by Weight of the fatty acid content of said material at a temperature between about 60 and about 175 C., heating the mixture of fatty material and carbonate to maintain it liquid at a temperature between 8 about 60 and about 175 C. until the reaction between said fatty acids and carbonate is substantially complete, and thereafter completing saponification of said material with an aqueous alkali metal hydroxide solution containing from 10% to about 50% by weight of said hydroxide.

8. A method according to claim 7 and wherein the reactants are preheated to increase the evaporation of water from the reaction mass during saponification.

9. The method of making a soap containing not more than about 15% by weight moisture which comprises reacting a fatty material composed of free fatty acid and a maximum of about 15% glycerides with a dry alkali metal carbonate in an amount sufficient to saponify 30% by weight of the fatty acid content of said material at a temperature between about 60 and about 175 C. to form a viscous dough-like mass, and treating said viscous mass with an aqueous alkali metal hydroxide solution containing between about 25% and 50% by weight of said hydroxide to complete saponification of said material.

10. The method of making a soap containing not more than about 15% by weight moisture which comprises mixing a fatty material essentially composed of free fatty acids and a maximum of about 15% glycerides with a sufiicient quantity of dry alkali metal carbonate to partially saponify the fatty acid content of said material, heating the mixture of fatty material and carbonate to maintain it in liquid condition at a temperature between about 60 and about 175 C. until the reaction between the fatty acid and carbonate is substantially complete, then cooling the reaction product to form a viscous dough-like mass, and thereafter treating the viscous mass with an aqueous alkali metal hydroxide solution containing between about 25 and 50% by weight of said hydroxide to complete saponification of said material.

11. A method according to claim 10 and wherein an excess of alkali is added in the second saponification step to cause the completely saponified product to break up into pellets.

12. A method according to claim 10 and wherein an excess of alkali is added in the second saponification step and the excess alkali is a sodium salt selected from the group consisting of silicates, phosphates and carbonates.

13. A continuous method of making a soap containing not more than about 15% by weight moisture which comprises reacting in a first stage a mixture of free fatty acids and a maximum of about 15% fatty acid glycerides with a quantity of dry metal carbonate sufficient to saponify 30%80% by weight of the fatty acid content of said mixture, heating the reaction mass in said first stage to maintain it in liquid condition at a temperature between about 60 and about 175 C., treating the resulting product in a second stage with aqueous caustic alkali having a concentration of 10% to about 50% by weight to complete the saponir'ication of the fatty acids and glycerides, and maintaining the temperature of the reaction mass in said second stage at at least C. to maintain a relatively high saponification rate in said second stage.

14. A method of producing a soap containing not more than about 15% by weight moisture, which comprises reacting a fatty acid material essentially composed of free fatty acids and containing up to 15 by weight of glycerides with a quantity of dry sodium carbonate sufficient to saponify approximately 60% of the free fatty acid content of said material at a temperature of 60 C. to C., and thereafter completing saponification of said material with a sodium hydroxide solution containing about 50% by weight of said hydroxide.

15. A method according to claim 14 and wherein an excess of alkali is used in the second stage saponification to cause the product to disintegrate into pellets.

(References on following page) 9 10 References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS Thomssen et 211.: Modern Soap Making, 1937, 904 520 m 4 190 MacNair-Dorland Company, N. Y. C., pages 170-172. 1,904,021 Weber et a1. Apr. 18, 1933 5 FOREIGN PATENTS 494,056 Great Britain of 1938 

1. THE METHOD OF MAKING A SOAP CONTAINING NOT MORE THAN ABOUT 15% BY WEIGHT MOISTURE WHICH COMPRISES REACTING A FATTY MATERIAL COMPOSED OF FREE FATTY ACIDS AND A MAXIMUM OF ABOUT 15% GLYCERIDES WITH A DRY ALKALI METAL CARBONATE IN AN AMOUNT SUFFICIENT TO SAPONIFY 30%-80% BY WEIGHT OF THE FATTY ACID CONTENT OF SAID MATERIAL AT A TEMPERATURE BETWEEN ABOUT 60 AND ABOUT 175* C., AND THEN COMPLETING SAPONIFICATION OF SAID MATERIAL WITH AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION CONTAINING FROM 10% TO ABOUT 50% BY WEIGHT OF SAID HYDROXIDE. 